Disc drives for magnetic discs are well known in the field of data storage for electronic computers. The conventional phonograph record is another example of information stored in the disc format. Recently numerous high density technologies have permitted the storage of audio or video information on discs. An optical disc system, in which a laser beam reads information from the disc, is one preferred method since there is no wear or tear on the disc surface. But in such audio and video disc systems, special care is required in the handling of the disc to avoid scratches or other damage to the surfaces of the disc. Due to the high information density, surface damage may interfere with the reading out of the information.
At present automatic disc players are being developed of the kind which have a slit into which the disc is inserted so as to be received by an automatic positioning mechanism. The positioning mechanism is required in order to engage the disc with a drive spindle to rotate the disc. The disc must also be centered on the drive spindle which typically requires the engagement of a centering hub with a central hole in the disc. Thus means are required for effecting the relative axial movement of the centering hub with respect to the disc and further means are required for clamping the disc to the drive spindle when the central hole of the disc is engaged with the centering hub. Clamping the disc to the drive spindle presents a particularly difficult problem since the clamping mechanism must not interfere with the insertion of the disc into the disc player. Moreover, the disc is typically rotated at high speed on the order of 200 to 1800 revolutions per minute, and it is especially important that the clamping mechanism reliably holds the spinning disc against the drive spindle.
It is preferable to have the drive spindle with its axis vertical and to have the disc located above the spindle so that the central portion of the disc sits on the drive spindle and so that the drive spindle solidly rests on its bearings. But then the clamping mechanism must be raised off of the disc in order for the disc to be disengaged from the drive spindle. This raising of the clamping mechanism presents a difficulty because the mechanism's own weight must be countered and further the clamping mechanism must freely rotate with respect to whatever means are used to lift off the clamping mechanism. This is a consequence of the fact that the clamping mechanism must rotate with the disc when the disc is clamped to the spindle, yet when the clamping mechanism is lifted off the disc and spindle, the clamping mechanism must be kept clear of the disc so as not to scratch the upper surface of the disc when the disc is inserted or ejected from the disc drive.